Passive RFID tags are highly reliable battery-less electronic devices primarily employed to streamline logistical and manufacturing processes. Passive RFID tags can be attached to physical objects that are either remote or are in motion, and provide dozens of bits of unique error-correctable identification. Higher performance RFID tags also include rewritable electronic memory and environmental transduction. For example, pressure RFID tags inside industrial tires automatically relay profiles to a central server that triggers maintenance, thus improving performance, reliability, and reducing replacement cost. Simpler identification RFID tags transmit a unique identification associated with the object in transit, for example a pallet load or a case of expensive fragrance.
In a typical RFID system, RFID tags (also referred to as transponders) are located on an asset to be tracked. A RFID reader (also referred to as an interrogator), which typically contains a radio frequency (RF) transceiver, when triggered, sends a radio frequency signal (an interrogation) towards the RFID tag. In a typical embodiment, the RF signal, also known as the carrier signal, initially supplies a voltage to the antenna coil of the RFID tag. The received voltage is rectified in the RFID tag to supply power for the RFID tag. The RFID reader modulates the carrier signal, using, in an exemplary embodiment, amplitude modulation (or AM modulation) to send data (such as a request for the RFID tag to provide information such as the RFID tag's identification number) to the RFID tag. The RFID tag responds by modulating the carrier signal and back scattering the modulated signal to the RFID reader.
The tags can either be active tags, which may transmit continuously or periodically, or passive tags, which transmit in response to an interrogation. Active tags are typically battery powered. Passive tags are typically powered without contact by the electrical or mechanical field generated by the reader.
When using an RFID system consideration might be given to the RFID tag to select for a given purpose. Typically, a user of RFID tags attempts to optimize certain properties of a RFID tag such as the range of the tag (maximum distance between the RFID reader and the RFID tag that communications can occur), the data rate of the tag and the cost of the tag. However, there is a complex relationship between these parameters and other parameters that are to be optimized.
As an example, FIG. 1 illustrates the dependencies of parameters within an optimization framework. In this example, data rate 102, range 104 and cost 106 are the parameters to be optimized and appear on the vertices of an optimization triangle. As can be seen in FIG. 1 these parameters depend on other factors. For example, range 104 is dependent on bandwidth, sideband formation, transmission power, wavelength used, antenna gain, the sensitivity to detuning, logic power, the efficiency of the voltage regulator and rectifier in the tag. Some of these parameters are constrained by regulations. For example, different countries allow RFID systems to operate in different frequency ranges and at different power levels. Some parameters are dependent on the semi-conductor fabrication technology used. For example, the operating voltage is dependent on the semiconductor fabrication technology, as is the capacitance and gate density of the integrated circuit of the RFID tag. Similarly, the cost 106 and data rate 102 are also affected by different parameters, as shown in FIG. 1, which in turn are affected by regulations, operating environment and semiconductor manufacturing techniques.
Therefore, it is desirable to develop an operational model for passive RFID tags that relate key parameter dependencies and develop a method for optimizing the design and implementation of RFID tags.